NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How Many Chronometers?
From: Tom Sult
Date: 2009 Sep 15, 06:22 -0500
From: Tom Sult
Date: 2009 Sep 15, 06:22 -0500
looks to me like $17 would give a perfectly adequate chronometer, especially when compared to early chronometers of sea faring days. Thomas A. Sult, MD IntegraCare Clinic www.icareclinics.com tsult@charter.net On Sep 15, 2009, at 4:22 AM, Gary LaPook wrote: > Based on our discussion, I became curious about the accuracy of > digital > watches and their suitability for use as chronometers so I went to my > local TARGET store and purchased three identical watches for $17.00 > each, the cheapest that they had. I set them and let them run for a > few > days and, as I expected, they each had different rates. Based on > this I > labeled them "A", "B", and "C" in the order of their rates starting > with > the slowest. I then reset them to UTC at 0121 Z on May 28, 2009. I > checked them against UTC from WWV eleven days later on June 8th and > found that they were all running fast by 2, 4 and 7 seconds > respectively > and I worked out their daily rates as .1818, .3636, and .6363 seconds > per day, respectively. > > On July 11th, 44 days after starting the test, the watches were fast > by > 9, 17 and 28 seconds. Using the rates determined in the first 11 days > the predicted errors would have been 8, 16 and 28 amounting to > errors in > prediction of 1, 1, and 0 seconds. If using these three watches for a > chronometer we could average the three errors and end up with only > a .66 > second error in the UTC determined by applying the daily rates to the > three displayed times after 33 days from the last check against WWV > which took place on June 8th. > > I determined new rates now based on the longer 44 day period of .2045, > .3864 and .6363 seconds per day, respectively. > > On September 15th at 0800 Z (per WWV), 110 days after starting the > test, I took a photo of the watches which I have attached. The photo > shows the watches fast by 21, 41 and 69 seconds but by carefully > comparing them individually with the ticks from WWV the estimated > actual > errors are 21.5, 41.8 and 69.0 seconds. Using the 44 day rates, the > predicted errors are 22.5, 42.5, and 70 seconds giving the errors in > the > predictions of 1.0, 0.7 and 1.0 seconds which, if averaged, would have > caused a 0.9 second error in the computed UTC after 66 days from the > last check against WWV on July 11th. > > If, instead, I used the 11 day rates then the predicted errors would > have been 20.0, 40.0, and 70.0 seconds which would result in errors of > prediction of -1.5, -1.8, and 1.0 which, if averaged, would cause and > error in the computed UTC of -0.6 seconds after 99 days from the last > check against WWV which would have been on June 8th in this example. > > From this experiment it appears that fifty one dollars worth of cheap > watches would give you a perfectly adequate chronometer. > > gl > > > >--~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---